A pupil stormed into a school and beat up and stabbed a teacher - but she was only given a police caution.

The female maths teacher, who the girl blamed for getting her expelled, had to go to hospital for her injuries after the frenzied attack in front of shocked students.

The girl of 14, who cannot be named, kicked and punched the woman to the ground and carried on the assault as she lay there.

Then she stabbed her face with a marker pen before using it to scrawl on her.

Two male members of staff had to drag the teenager off the teacher, who had serious bruising to her face and cuts to her legs. The pupil is understood to have been furious at her expulsion after she was accused of trying to steal the same teacher's keys and mobile phone.

A girl of 15, who witnessed the incident, said: "The door flew open and she ran at the teacher. It was horrible.

"That girl is a complete psycho but really strong. She was on top of the teacher - no one could do anything."

But amazingly when police were called, the student - a known troublemaker - was issued with only a caution after the incident last Friday at the Westwood Language College in Upper Norwood, South London. Police said: "A girl was arrested for assault.

After a thorough investigation, she was given a final warning for this offence." A parent whose 14-year-old daughter attends the school said: "It's a disgrace. This girl should be prosecuted. She's clearly a threat to all girls."

Incredibly, the girl's mother had rung the school earlier in the day to warn that her daughter was on her way.

But one teacher claimed nothing was done to stop the girl confronting the victim.

The girl had been transferred to another nearby school earlier this year because of her unruly behaviour - but was booted out in three weeks because she had "no respect for authority".

Headteacher Margaret Hedley said: "We have robust policies to deal with such incidents."